Assisted Migration and Forest Trees Adapting to Climate Change: NY Times Article

Julio Cruz on Thursday works on the Forest Service’s plan to plant about 150,000 trees on land ravaged by the Hayman fire in the Pike National Forest. The plan also aims to protect Front Range water supplies. From the Denver Post.

You’ve gotta love this business.  In 1980 at the Fifth North American Forest Biology Workshop, I remember a fellow geneticist talking about how climate change was going to cause trees to die out because they couldn’t move north due to uninhabitable spaces for them compared to post-glaciation (say fields instead of forests in the Midwest). That was 40 years ago. I remember so clearly because I remember thinking “but we didn’t have pick-up trucks then and seeds could fall into the back,  and get moved across those spaces.”  And that’s if we didn’t intentionally move them across spaces and plant them, something people are thinking about and now doing.

Here we are in 2019 and here is an article in the NY Times about moving tree species north, now called “assisted migration.” It’s pretty interesting. Here are a few quotes.

As a cautionary tale, Mr. Riely looks to the forest collapse that struck near Denver some years back. Conditions in the Rockies differ substantially from those in Rhode Island; still, he calls it “a water supplier’s nightmare.”

In the 1990s, dry spells, insects and disease began killing trees there. In 1996 and 2002, ferocious fires tore through. Then the rains came. Flash floods carried dark, ash-filled silt and debris into Denver’s reservoirs, clogging them.

So in 2010, Denver Water began replanting the mountainsides, making the forest more drought-resistant by spacing trees farther apart and reducing competition for water. Opening the forest canopy allowed other kinds of plants, which also prevent erosion, to grow as well.

I’m not sure I would agree that the forest “collapsed” prior to say, the Hayman Fire.  But it certainly makes sense to plant trees farther apart in conditions where other trees are unlikely to fill in, and otherwise planted ones might need to be thinned at some point in the future. I wonder about the idea of  “opening the forest canopy” after Hayman, as it was and is pretty open in a lot of places. Like there are no living trees. See the photo above.

Another interesting thing about this article is that it talks about moving species, and planting species in different microclimates, but not much about using different genetic sources of the same species. That approach would possibly have less disruptive effects on associated organisms in the area.  As the concern is mentioned in the story:

Some worry about the unintended consequences of shuffling plants and animals around and that the approach will become widely adopted. “Moving species is the equivalent of ecological gambling,” said Anthony Ricciardi, a professor of invasion ecology and environmental science at McGill University in Montreal. “You’re spinning the roulette wheel.”

In the world of forest genetics, there have been many plantings of different seed sources through time in different places. The last I heard, people were taking advantage of this knowledge where it is available in terms of moving sources.  I also remember the effort to grow eucalypts in Florida for biomass (pre-energy) and the hundred year freezes that knocked them out in the 80’s.. Here’s a link to the history by Don Rockwood at the University of Floriday. You can argue that eucs are a different beast because they’re not from North America but still…things can grow well for a while and then.. not so much.

Matching Eucalyptus species to Florida’s diverse weather and soils is challenging. Historically defined climatic regions based on average low temperatures or numbers of freezes provide some broad guidelines, but annual aberrations such as the three 100-year freezes in the 1980s [11], extended cold periods of the 2010-11 winter, and the abrupt freezes of the “warm” winter of 2011-12 profoundly influence freeze susceptibility of all young eucalypts. Rainfall patterns with unpredictable, extended dry spells make Florida’s summer rainfall climate highly variable and difficult for successful planting and early growth.

Finally, I think it’s important to note that worrisome invasive tree pests continue to be imported and expand in the US. So you’ve got unpredictability of different kinds (and climate and pests can interact) over a period of a tree’s lifespan (a hundred years or more). I can see why people might try some things, or wait and see.

5 thoughts on “Assisted Migration and Forest Trees Adapting to Climate Change: NY Times Article”

  1. Some of the comments on the article are interesting, such as:

    Princeton, NJ April 25

    As a climate scientist, I’d like to provide some further context.

    The latest data on global vegetation cover change, published last year in Nature by Song et al. (U Maryland), indicates that:

    “Here we analyse 35 years’ worth of satellite data and provide a comprehensive record of global land-change dynamics during the period 1982–2016. We show that—contrary to the prevailing view that forest area has declined globally—tree cover has increased by 2.24 million km2 (+7.1% relative to the 1982 level). This overall net gain is the result of a net loss in the tropics being outweighed by a net gain in the extratropics.”

    If one looks at figure1 in this article, for the US in particular, one can see that forest cover has declined in the West, increased in the East.

    Globally, there is little doubt that over the last 3-4 decades the Earth has been “greening” – not in every region, but on average, yes. Some of the driving factors include direct human land changes (e.g., crop abandonment in Russia, active reforestation in China), warming at high latitudes, CO2 fertilization.

    The big question is whether this will continue in the future, or reverse as the effects of climate change become more prevalent. This also says nothing about ongoing species composition changes (as discussed in this article).

  2. These types of discussions/articles are leading to a new look at seed zones based on climatic factors instead of rigid boundaries on the ground. There is a list of recorded webinars here for the eastern US seed zone forum:

    For the western US, there is the seedlot selection tool:
    (there is a recorded webinar here:

    • Thanks, Anon. — excellent resources.

      I’m curious if there is a list or database of tree species that are able to do well outside their native zones. Radiata (Monterey) pine, for example, grows well in many areas with climates very different than its native central California coast. According to the US Forest Service, radiata is cultivated for timber in Maui, Hawaii and is also widely planted for timber in Australia, New Zealand, South Africa, Chile, Spain, and the British Isles. Likewise, many eucalypts are grown for timber and fiber far from their native ranges in Australia.

      • Usually in the old days folks would do species trials if they were interested in trying out different species. Then if they found one they would do provenance trials of different seed source areas. Then if the rotation were short enough (30-50 years) you could cross the trees that do the best in their new environment, and you would have populations of that species adapted to their new environment.

        When I was a Berkeley forest genetics student in the 70’s, our group was very worried about New Zealand and radiata pine and some non-native pest wiping them all out. Working with forest trees over long periods of time is a good way to learn humility about the natural world.

    • Just to keep in mind, those are folks’ best estimates of what to plant and not ground-truthed, and ground truthing may take 50 or more years with forest trees, by which time the climate could have changed more and potentially unpredictably. Which is not to denigrate these efforts but to put them in perspective.


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